From 8b93d1d7dbd578fd296e70008b29c0f62d09d7cb Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Thu, 12 Aug 2021 15:14:10 +0200 Subject: [PATCH] drm/shmem-helper: Switch to vmf_insert_pfn MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit We want to stop gup, which isn't the case if we use vmf_insert_page and VM_MIXEDMAP, because that does not set pte_special. The motivation here is to stop get_user_pages from working on buffer object mmaps in general. Quoting some discussion with Thomas: On Thu, Jul 22, 2021 at 08:22:43PM +0200, Thomas Zimmermann wrote: > Am 13.07.21 um 22:51 schrieb Daniel Vetter: > > We want to stop gup, which isn't the case if we use vmf_insert_page > > What is gup? get_user_pages. It pins memory wherever it is, which badly wreaks at least ttm and could also cause trouble with cma allocations. In both cases becaue we can't move/reuse these pages anymore. Now get_user_pages fails when the memory isn't considered "normal", like with VM_PFNMAP and using vm_insert_pfn. For consistency across all dma-buf I'm trying (together with Christian König) to roll this out everywhere, for fewer surprises. E.g. for 5.14 iirc we merged a patch to do the same for ttm, where it closes an actual bug (ttm gets really badly confused when there's suddenly pinned pages where it thought it can move them). cma allcoations already use VM_PFNMAP (because that's what dma_mmap is using underneath), as is anything that's using remap_pfn_range. Worst case we have to revert this patch for shmem helpers if it breaks something, but I hope that's not the case. On the ttm side we've also had some fallout that we needed to paper over with clever tricks. v2: With this shmem gem helpers now definitely need CONFIG_MMU (0day) v3: add more depends on MMU. For usb drivers this is a bit awkward, but really it's correct: To be able to provide a contig mapping of buffers to userspace on !MMU platforms we'd need to use the cma helpers for these drivers on those platforms. As-is this wont work. Also not exactly sure why vm_insert_page doesn't go boom, because that definitely wont fly in practice since the pages are non-contig to begin with. v4: Explain the entire motivation a lot more (Thomas) Acked-by: Thomas Zimmermann Signed-off-by: Daniel Vetter Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210812131412.2487363-2-daniel.vetter@ffwll.ch --- drivers/gpu/drm/Kconfig | 2 +- drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++-- drivers/gpu/drm/gud/Kconfig | 2 +- drivers/gpu/drm/tiny/Kconfig | 4 ++-- drivers/gpu/drm/udl/Kconfig | 1 + 5 files changed, 7 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index 0d37235..314eefa 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -211,7 +211,7 @@ config DRM_KMS_CMA_HELPER config DRM_GEM_SHMEM_HELPER bool - depends on DRM + depends on DRM && MMU help Choose this if you need the GEM shmem helper functions diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index a619463..cc96d1c 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -542,7 +542,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) } else { page = shmem->pages[page_offset]; - ret = vmf_insert_page(vma, vmf->address, page); + ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page)); } mutex_unlock(&shmem->pages_lock); @@ -612,7 +612,7 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) return ret; } - vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND; + vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND; vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); if (shmem->map_wc) vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot); diff --git a/drivers/gpu/drm/gud/Kconfig b/drivers/gpu/drm/gud/Kconfig index 1c8601b..9c1e61f 100644 --- a/drivers/gpu/drm/gud/Kconfig +++ b/drivers/gpu/drm/gud/Kconfig @@ -2,7 +2,7 @@ config DRM_GUD tristate "GUD USB Display" - depends on DRM && USB + depends on DRM && USB && MMU select LZ4_COMPRESS select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig index d31be27..1ceb93f 100644 --- a/drivers/gpu/drm/tiny/Kconfig +++ b/drivers/gpu/drm/tiny/Kconfig @@ -44,7 +44,7 @@ config DRM_CIRRUS_QEMU config DRM_GM12U320 tristate "GM12U320 driver for USB projectors" - depends on DRM && USB + depends on DRM && USB && MMU select DRM_KMS_HELPER select DRM_GEM_SHMEM_HELPER help @@ -53,7 +53,7 @@ config DRM_GM12U320 config DRM_SIMPLEDRM tristate "Simple framebuffer driver" - depends on DRM + depends on DRM && MMU select DRM_GEM_SHMEM_HELPER select DRM_KMS_HELPER help diff --git a/drivers/gpu/drm/udl/Kconfig b/drivers/gpu/drm/udl/Kconfig index 1f497d8..c744175 100644 --- a/drivers/gpu/drm/udl/Kconfig +++ b/drivers/gpu/drm/udl/Kconfig @@ -4,6 +4,7 @@ config DRM_UDL depends on DRM depends on USB depends on USB_ARCH_HAS_HCD + depends on MMU select DRM_GEM_SHMEM_HELPER select DRM_KMS_HELPER help -- 2.7.4